Modular glass covered solar cell array

ABSTRACT

A radiation tolerant solar cell array module which can be efficiently assembled into a larger solar panel to generate power for a spacecraft the module includes at least first and second single-crystal solar cells. The first and second solar cells have front sides and back sides. At least one of the solar cells has a shallow junction N on P structure. A first contact is formed on at least the back side of the first solar cell. A second contact formed on at least the back side of the second solar cell. A conductor is in electrical communication with the first contact and the second contact. A substantially transparent ceria-doped cover overlays at least a portion of each of the solar cells. The cover remains substantially transparent when exposed to an AM0 space radiation environment. A substantially transparent adhesive is situated between the cover and the solar cell portions. The adhesive remains substantially transparent when exposed to a space radiation environment.

BACKGROUND OF THE INVENTION

1. Field of The Invention

The present invention relates to solar cells. In particular, theinvention relates to methods and apparatuses for efficient packaging ofsolar cells for space applications.

2. Description of The Related Art

Photovoltaic cells, commonly called solar cells, are well-known deviceswhich convert solar energy into electrical energy. Solar cells have longbeen used to generate electrical power in both terrestrial and spaceapplications. Solar cells offer several advantages over moreconventional power sources. For example, solar cells offer a cleanmethod for generating electricity. Furthermore, solar cells do not haveto be replenished with fossil fuels. Instead, solar cells are powered bythe virtually limitless energy of the sun. However, the use of solarcells has been limited because solar cells are a relatively expensivemethod of generating electricity. Nonetheless, the solar cell is anattractive device for generating energy in space, where low-costconventional power sources are unavailable.

Typically, solar cells manufactured for space use have been of fairlysmall dimensions. Commonly, solar cells have had dimensions of 4 cm×6 cmor less. In space applications, hundreds or thousands of the small solarcells are interconnected together to form large solar arrays. In atypical manufacturing process, a solar cell manufacturer delivershundreds or thousands of separate, unconnected, solar cells to a solararray assembler. Often, the solar cell manufacturer mounts a coverglassover each cell to protect the cells against space radiation and otherenvironmental conditions. Alternatively, the solar cell manufacturer mayship bare cells to the array assembler. The array assembler then mustprovide the coverglass. The array assembler also interconnects theindividual cells into large, suitably sized panels.

The use of individual coverglasses for each cell has severaldisadvantages. For example, it is expensive and time consuming to mounta separate coverglass on each cell. In addition, the use of small cellsincurs several disadvantages. For example, the smaller the cell size,the more cells are required to form an array of a given size. The morecells which must be assembled, the greater the manufacturing costs. Inaddition, each cell must be tested individually before being assembledinto a larger array. Thus, the greater the number of cells required, thegreater the number of tests which must be performed. Furthermore, thesmaller the cells, the greater the total cell edge length (i.e. thelength of all cell sides summed together) for a given array size. Celledges are typically prone to damage. Thus, the greater the total edgelength, the more likely that at least some cells will be damaged duringthe manufacturing, transport, and assembly of the cells.

SUMMARY OF THE INVENTION

One preferred embodiment of the present invention is a modular, glasscovered solar cell array suitable for use in space. The modular, glasscovered solar cell array includes at least physically and electricallyinterconnected solar cells. At least a portion of both cells are coveredby a common, substantially transparent cover. The transparency of thecover will not substantially degrade when exposed to a space radiationenvironment. In one embodiment, at least one cell is comprised ofsingle-crystal silicon. In another embodiment, at least one cell iscomprised of GaAs. In yet another embodiment, at least one cell iscomprised of multijunctions.

In one embodiment of the present invention, at least one cell has anarea of at least 100 cm². In another embodiment, at least one cell is atleast 150 μm thick. In still another preferred embodiment, at least onecell is thinner than 150 μm.

In another embodiment of the present invention, the solar array cellsare interconnected by at least one conductor mounted on the backs of thecells. In still another embodiment, at least one cell has at least onecontact for receiving the conductor. The contact wraps from a first sideof the cell to a second side of the cell. In another embodiment, atleast one cell has at least one contact for interconnection to at leastone other solar cell array.

In one embodiment, the solar cell array includes at least one bypassdiode mounted to at least one surface of one of the cells. In anotherembodiment, the solar cell array includes contacts for connection to atleast one externally mounted bypass diode.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, advantages, and novel features of the inventionwill become apparent upon reading the following detailed description andupon reference to accompanying drawings in which:

FIG. 1a illustrates one embodiment of a solar cell front side;

FIG. 1b illustrates one embodiment of a solar cell back side;

FIG. 1c illustrates one embodiment of a solar cell having wrap aroundcontacts;

FIG. 2 illustrates one embodiment of a standard power module;

FIG. 3 illustrates components of one embodiment of the standard powermodule;

FIG. 4 illustrates the results of a power density tradeoff analysis;

FIG. 5 illustrates the results of a cost versus coverglass quantitytradeoff analysis;

FIG. 6 illustrates the results of a cost versus coverglass coatingtradeoff analysis;

FIG. 7 illustrates the results of a cost versus adhesive mass tradeoffanalysis;

FIG. 8 illustrates the results of a radiation analysis for one relevantoperating environment.

FIG. 9 is a graph illustrating mission fluence versus shielding;

FIG. 10A illustrates one embodiment of an array of interconnectedstandard power modules;

FIG. 10B is a detailed diagram of a portion of the interconnectedstandard power modules of FIG. 10A.

FIG. 11 illustrates one embodiment of a solar cell manufacturingprocess; and

FIGS. 12A, B illustrate one embodiment of a standard power modulemanufacturing flow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As illustrated in FIGS. 2 and 3, in one preferred embodiment a baselinemodular, glass covered solar array 200, which is interchangeably calleda standard power module (SPM), consists of a solar cell circuit matrixthat can be readily used to build up a variety of array sizes. In apreferred embodiment, the SPM configuration consists of:

A large area (˜20 cm×30 cm) ceria doped borosilicate coverglassmicrosheet 202, nominally 100 μm thick, which provides radiationresistant shielding for charged and uncharged particles. One skilled inthe art will understand that other suitable coverglass materials anddimensions can be used as well.

Six large area (10 cm×10 cm) silicon solar cells 100, are approximately200 μm thick. A preferred embodiment of a solar cell is illustrated ingreater detail in FIGS. 1a-1c. The solar cells each have at least onespace qualified NIP wraparound contact 102, although otherconfigurations may be used as well. In a preferred embodiment, eachsolar cell has two contacts 102, 104, one for each cell doping polarity.

Two silver-plated Invar ribbon interconnectors 206, are approximately 50μm thick, and may be welded to each solar cell 100 to provide spacequalified thermally matched series connection. One skilled in the artwill understand that other interconnect technologies, such asmechanically bonding, crimping and soldering may also be used.

As illustrated in FIG. 3, transparent silicone adhesive 300, nominally50 μm thick, bonds the solar cell circuit to the coverglass 202 andprovides a space qualified non-darkening resilient interface.

In one preferred embodiment, the solar cell design is space qualifiedwith a single-crystal silicon design. However, one skilled in the artwill understand that other technologies, including GaAs/Ge andmultijunction solar cells, can be used as well. In the preferredembodiment, the materials and the cell are optimized for performance inan AM0 spectrum (the spectrum found at Earth's orbit around the sun,outside of Earth's atmosphere) and the space radiation environment. Asillustrated in FIGS. 1c, a shallow junction N on P structure 106 whichprovides satisfactory radiation resistance may be used. By contrast,terrestrial silicon cells have lower radiation resistance because theyuse deep junctions to prevent punch through of the screen printedcontacts. For extraterrestrial applications, the preferred base siliconmaterial is space qualified, Czochralski grown, boron doped,single-crystal silicon with a base resistivity of 1-3 ohm-cm. Thisresistivity is a compromise (radiation resistance vs. initial power) formany missions that don't see radiation fluences greater than about 3E15e/cm² (1 MeV equivalent) where 10 ohm-cm material becomes advantageous.The silicon wafer of the preferred embodiment has been designed toprovide cost reductions compared to conventional designs, while at thesame time maintaining those attributes that are important formaintaining radiation resistance, such as the resistivity and minoritycarrier lifetime.

As discussed above, GaAs/Ge and multijunction solar cells may be used inthe SPM instead of silicon solar cells. The GaAs/Ge and multijunctionsolar cells, such as those manufactured by TECSTAR, can provideefficiencies greater than 24%.

From a reliability standpoint, an important design concern for solarcells is the contact characteristics. Preferably, both electrical andmechanical integrity are maintained throughout the mission even aftermany thermal stress cycles. To aid reliability, TiPdAg and AlTiPdAg backsurface reflector (BSR) evaporated contacts may be used on silicon-typecells. To reduce costs, a metal shadow mask may be used, rather thanmuch more expensive photolithographic techniques which can be used aswell. A workable combination, consisting of bimetallic masks with narrowslots may be used. Mechanical fixturing with permanent magnets may beused to hold the masks firmly against the cell surface during metalevaporation.

In the preferred embodiment, the AlTiPdAg contact on the back side ofthe solar cell has an evaporated aluminum BSR layer under the TiPdAgcontact to reflect the long wavelength light which consequently reducesthe absorptivity (α) to 0.71.

In a preferred embodiment, a two-sided wraparound (WA) contactconfiguration 102 as shown in FIGS. 1a-1c is used due to its manyadvantages. First, the contact "pick-off" at two opposite ends, halvesthe parasitic series resistance losses associated with 10 cm dimensions.Also, because the contacts 102, 104 are located primarily on the back ofthe cell 100, the front contact area is reduced, resulting in anincreased active area. With all the terminal contacts 102, 104 on theback surface, the coverglass can cover the entire front surface, withoutintroducing stress risers, resulting from top-to-bottom interconnects.The coverglass also provides fall cell protection from atomic oxygen andhigh energy particle radiation effects. In the preferred embodiment, thedesign provides a "give away area" on the rear surface below 5%, addingless than 1% to the resistive losses.

As illustrated in FIGS. 1a-1c, in a preferred embodiment, the contact102 is electrically coupled to N- material, while the contact 104 iselectrically coupled to P+ material.

One embodiment of the front of the cell 100 illustrated in FIG. 1a has adimension D1 of approximately 10 cm, a dimension W1 of approximately 10cm, a bus bar width dimension X1 of approximately 0.1 cm, and a bus barspacing of approximately 4.57 cm. One embodiment of the back of the cell100 illustrated in FIG. 1b has a contact width dimension T1 ofapproximately 0.2175 cm, and an N channel contact length dimension L1 ofapproximately 6.55 cm, and a P channel contact length L2 ofapproximately 2.29 cm.

The estimated conversion efficiency of one embodiment of a 10 cm×10 cm,WA contact cell 100, is approximately 12.1% (1,367 W/m², AM0). Thisestimate is based on data from a prior art 13.7% efficient 4 cm×6 cmcells with dual antireflection coating derated by the following factors:

0.969 to include the effects of large cell area, series resistance andcontact area losses;

0.945 to allow for the use of a single low cost layer CVD AR-coating;

0.980 for reduced area (obscuration), resulting from the use of low costshadow masks;

0.985 for the WA contact effects, series losses from the give-way area,and shunt losses at the WA edges.

Typically, having fewer, larger cells reduces cost since the use oflarger cells means there are less parts to handle, less testing, lesswaste area and consequently less attrition. Thus, the use of 10 cm×10 cmcells, such as are used in terrestrial applications, as compared with 4cm×6 cm or 8 cm×8 cm typically used in space applications, are used.This size is also compatible with the size ingots and the mechanizationequipment available.

To minimize weight, the solar cell should preferably be as thin aspractical, and 62 μm silicon cells have been fabricated and used to makeflight qualified arrays, and may be used in the present invention.However, without incorporating a costly back surface field (BSF) design,there is a significant power loss for cells thinner than 150 μm. Thus,in one embodiment, a 200 μm cell thickness is used to minimize breakagelosses associated with large area cells and to increase delta efficiencyby 6%. This performance versus weight trade-offs is discussed further inthe SPM discussion below.

In one embodiment, the solar cell antireflection coating is a singlelayer TiOx chemical vapor deposition (CVD) coating instead of the moreexpensive evaporated dual AR coatings. Both coating types can be used,have been space qualified, and have space flight heritage. However, inrecent years, the additional Isc (short circuit current) performanceadvantage has been desired in spite of the additional costs andexpensive evaporator equipment encountered. In order to reduce cost andincrease throughput levels, the CVD method to form the AR coating inused in one embodiment. This coating will not delaminate or degrade thecell's mechanical integrity or electrical performance when operated overthe specification environment and mission life.

Under dark reverse testing to 110% of Isc for 20 minutes, typical WAcontact cells measured reverse voltages of 18-20 Volts. The use ofbypass diode protection against reverse voltages is discussed below.

A summary of the selected solar cell physical and performancecharacteristics is presented in Table 1. These characteristics were usedto predict on-orbit performance for the mission life.

                                      TABLE 1                                     __________________________________________________________________________    The Solar Cell Outputs 1.62 Watts BOL                                           (12.1% Efficiency) In Production Quantity                                   __________________________________________________________________________                                     Weld Pull                                        Resistivity   Strength                                                       Type (ohm-cm) Size (cm) Weight (gm) (gm)                                   __________________________________________________________________________      Physical Silicon N/P, 1-3 10 × 10 × 0.02 5.20 ≧300                                                Characteristics BSR                  __________________________________________________________________________       Front Back  Solar Emittance                                                   Contacts Contacts AR-Coating Absorptance (+ cover)                         __________________________________________________________________________      Physical TiPdAg, AlTiPdAg, TiOx 0.71 0.87                                     Characteristics Wraparound BSR                                              __________________________________________________________________________       Isc Voc Imp Vmp Pmp V.sub.Rev                                                 (mA) (mV) (mA) (mV) (mW) -1.1 Isc (V)                                      __________________________________________________________________________      Electrical Prop. 3700 584 3375 480 1620 18-20                                 (AM0, 28° C.)                                                        __________________________________________________________________________       Isc Voc Imp Vmp                                                               (μA/cm.sup.2 ° C.) (mV/° C.) (μA/cm.sup.2 °                                             C.) (mV/° C.) Pmp (%/.degre                                            e. C.)                                __________________________________________________________________________      EOL Temp. +36 -2.28  +35 -2.02  -0.37                                         Coefficients                                                                  (28-60° C.)                                                          __________________________________________________________________________       Fluence/cm.sup.2 Isc Voc Imp Vmp Pmp                                       __________________________________________________________________________      1 MeV 1E14 0.94 0.965  0.935 0.96  0.90                                       Radiation 5E14 0.86 0.93  0.85 0.925 0.785                                     2E15 0.76 0.885 0.76 0.885 0.675                                           __________________________________________________________________________

As previously discussed, a preferred embodiment baseline SPM design isshown in FIGS. 2 and 3 and consists of six, 10 cm×10 cm, 200 μm BSRsilicon solar cells 100 interconnected with 50 μm thick silver-Invarribbons 206. However, even larger area coverglass sizes may be used.Each SPM 200 is covered with a 100 μm thick, cerium oxide coverglass 202which is bonded to the cells with Nusil CV7-2500 adhesive 300. Componentselection was based on system trade studies that evaluated electricaland mechanical performance, mass, reliability, manufacturability, size,cost, schedule and heritage. The preferred embodiment of the baselineSPM design advantageously has the following properties:

Reduction in piece parts--higher reliability and lower cost;

Low mass--minimal coverglass adhesive, cell and coverglass mass, asillustrated in FIG. 4;

Manufacturable, efficient design--all interconnections are made on theback side of the SPM 200, as illustrated in FIG. 3; However, in otherembodiments, the interconnections can be made on other SPM surfaces.

Space qualified components

Performance parameters are well characterized.

In one embodiment of the SPM 200 illustrated in FIG. 2, the SPM 200 hasa length Y2 of approximately 30.17 cm, a width Y3 of approximately20.135 cm, and a typical cell gap and edge spacing Y1 of approximately0.025 cm.

The cell and coverglass trades for the SPM 200 are illustrated in FIG. 4which shows an approximate power to mass ratio of 100 Watts/kg at End ofLife (EOL) for the 0.020 cm/0.010 cm cell/coverglass thicknesscombination. The power density (W/kg) studies were performed to selectthe coverglass/cell thickness that would provide an optimum W/kg. Asshown in FIG. 4, the 0.015 cm/0.010 cm and 0.020 cm/0.010 cm cover andcell design options provide significantly higher values than the othercombinations. These two combinations were subsequently evaluated basedon manufacturability (yields) and the net cost of producing all of therequired SPMs. This analysis showed that while the 0.015 cm/0.010 cmcombination had a higher W/kg, it had a higher manufacturing cost due tolower expected yields than the 0.020 cm/0.010 cm combination. Therefore,based on its better $/kg ratio, 0.020 cm/0.010 cm is used in onepreferred embodiment. However, other combinations may be used as well.Table 2 below provides an SPM metric in terms of power, mass and areafor one particular design.

                  TABLE 2                                                         ______________________________________                                        A Preferred Embodiment SPM Provides High Power Densities                                       BOL      EOL                                                 ______________________________________                                        SPM Power (W)    9.62     5.29                                                  Area (m.sup.2) 0.0609 0.0609                                                  Mass (Kg) 0.05315 0.05315                                                     W/Kg 181 100                                                                  W/m.sup.2 158 87                                                            ______________________________________                                    

One preferred embodiment of the WA cell configuration allows for lowcost SPM manufacturing. Manufacturing operations may be performed withthe solar cells face side down for glassing, interconnecting, testingand marking. This approach reduces handling and greatly increasesthroughput. Another advantage of the preferred embodiment baselined cellis the interconnect. The interconnect may be a low cost silver-platedInvar ribbon formed for stress relief as part of the automation processand then welded to each cell of the SPM. The silver-plated Invarinterconnect material has a thermal coefficient of expansion which isclosely matched with silicon. This reduces weld and thermal elongationstresses resulting in a highly reliable interconnection. The stressrelief has been designed to absorb the 0.008 cm movement within the SPMand the 0.051 cm movement between SPMs. In one embodiment, theinterconnect is protected from the effects of atomic oxygen by thedesign of the SPM which shelters the interconnects by covering them withthe solar cell, cover adhesive and coverglass. Techniques other thanwelding may be used to attach the interconnects. By way of example,soldering or crimping techniques may be used as well.

The coverglass used in one preferred embodiment was selected by size,thickness and the need for coatings. FIG. 5 depicts the reduced costsavings of more than 71% by processing six cells under one piece ofglass as compared to fabricating an assembly of one cell with one pieceof glass. However, larger pieces of glass with a greater number of cellsare feasible. FIG. 6 provides the results depicting the cost advantageof approximately 35 percent by using uncoated glass versus coated glassexpressed in terms of dollars per watt at end-of-life. However,performance enhancements can be gained with the use of antireflective(AR) coatings with possible increased cost and added complexity atprocessing (having to keep track of the coated side). Coverglassperformance experiments have been conducted, and the results show theuncoated coverglass provides a one percent gain as compared to the baresolar cell which is attributable to the improved optical match of thecover overlaid on the cell. It is also possible to use a coverglass thathas increased rigidity when treated by a process called "toughened." Thetoughened glass process is widely used for military aircraft windshieldapplications and involves cutting the coverglass to it's final size,then chemically treating it to replace the sodium ions with potassiumions.

Atomic oxygen erosion of the coverglass will be less than 1 micron whenexposed to 1.5×10⁻²¹ A/cm². By analysis, one can calculate that even amore reactive material such as Teflon, which has a reaction efficiencyof <0.05×10⁻²⁴ cm³ /atom, would lose approximately 0.75 micron. Using aglass with no antireflection coating, as in one preferred embodiment,ensures that an adverse optical property change will not occur.

FIG. 7 shows that while EVA adhesive represents a significant costreduction (approximately 5.4 times) over CV7-2500, this growth in costonly affects the overall SPM cost by 2%. However, the mass increaseaffects the overall SPM by more than 6%. In one preferred embodiment,the lowest mass approach is used. CV7-2500 also has the advantage ofbeing space qualified and meets outgassing requirements where EVA isstill in the "experimental" stage for space use. Nonetheless, in anotherpreferred embodiment, EVA may be used as well.

One preferred embodiment of the SPM design facilitates SPM integrationinto large solar arrays. In a preferred embodiment, silver-plated Invarinterconnects protrude from the positive and negative edges of the SPMto allow for welding of the interconnects between each module. Theadvantage of this approach is that all SPM level interconnecting isaccomplished by overlapping the interconnect tabs and welding orsoldering them together. The SPMs are sized and configured to allow forrobotic intervention for a convenient pick and place operation.

FIG. 10A illustrates multiple SPMs 200 serially connected into a largerarray 1000, thereby providing higher output voltages than are achievableif the SPMs were connected in parallel. The array may optionally beprotected using external diodes 1002. In an alternative embodiment, theSPMs may be connected in parallel and the diode may be mounted withinthe SPMs.

FIG. 10B is a detailed diagram of a portion 1004 of the interconnectedstandard power modules of FIG. 10A. Interconnects 206 couple the Nchannel contacts 102 of one cell 100 to the P channel contacts of theadjoining cell.

In one preferred embodiment, silicon solar cells are used because theyhave the inherent capability to withstand reverse bias voltagesexperienced when cells in strings are partly or totally shadowed. Manysatellites have flown without bypass diode protection, but it iscustomary to include a bypass diode connected across several siliconcells to prevent overheating or degradation of shadowed cells.

While bypass diodes may not be required, in one preferred embodiment,bypass diode protection is provided at the array level or on the cellsthemselves. When a bypass diode is mounted on a cell, the diode istypically mounted onto a cell surface. In one embodiment, placing onebypass diode externally for every 20 cells in series (10 SPMs) serves toprotect the cells from degradation after the shadow is removed.

In another preferred embodiment, the solar cells are screened toidentify and reject cells having reverse bias problems, so that nobypass diodes are required.

A preferred embodiment of the SPM has excellent on-orbit performancecharacteristics. Performance predictions indicate that the EOL on-orbitpower-to-mass ratio will be 100 W/kg with an areal power density of 87W/m². These levels of performance translate into significantsystem-level benefits. The array mass savings can be used to increasethe payload mass and augment the capacity of the revenue-generatingcommunications systems. The areal power density performance enables asmaller area array, which reduces on-orbit drag, also reducing the fuel(and mass) that needs to be carried for station-keeping.

Power Analysis

A power analysis, presented in Tables 3A and 3B, uses typical lossfactors, including Af--the array-level loss factor of 0.938. The P_(SPM)(EOL, on-orbit) and P_(STC) (deliverable configuration) values arehighlighted in the analysis, and the Rf, Sf, Af, and Tfn factors areidentified. The P_(STC) value is based on SPM operation at the maximumpower point. This value may be for acceptance testing and operation atvoltages other than the maximum power point. For example, P_(STC) wouldbe 9.064 W (5.80% reduction) if SPM testing is conducted at:

    Vtest=0.9*Vmp(STC)=0.855 V.

The cell dimensions are effective dimensions for a rectangular cellhaving the equivalent area to a preferred embodiment of the cell havingcropped comers. A coverglass insertion factor of 1.01 is used. Thisvalue results from improved optical coupling to the single-layerAR-coated cell.

The temperature coefficients used are end-of-life values, and areapplied in the analysis after all the life factors have been taken.These values were determined from Figures 3.15-3.18 of the JetPropulsion Laboratory (JPL) Solar Cell Radiation Handbook (JPLPublication 82-69). The radiation factors are discussed further below.The UV darkening factor is based on similarity. The operatingtemperature was determined iteratively.

Radiation Analysis

The following process was used to determine the radiation effects on SPMperformance. This method is based on the Solar Cell Radiation Handbook.

Typical energy spectra for charged particle environments were enhancedby interpolating energies for which radiation damage coefficients aredefined by JPL. Energy spectra values are shown in FIG. 8 for relevantenvironments, trapped electrons, trapped protons, and solar protons.This is done to increase the resolution and accuracy of the subsequentcalculations for equivalent radiation fluence.

These enhanced spectra were then correlated with the JPL damagecoefficients for all values of shielding for which coefficients aredefined to determine the equivalent 1 MeV electron fluence. This wasdone for all relevant environments both for Isc-Voc and Pmax solar cellparameters. The results are presented in FIG. 9. The trapped protonenvironment is dominant. This data was used for the cell and coverglassthickness trade studies to determine optimum power-to-mass ratio for thepreferred embodiment of the SPM design.

                                      TABLE 3A                                    __________________________________________________________________________    The SPM Provides 9.62 Watts BOL and 5.29 Watts EOL                            __________________________________________________________________________    SOLAR CELL:  BSR2       CELL THICKNESS (cm):                                                                       0.020                                      DIMENSIONS   COVER THICKNESS (cm): 0.010                                      (in):** 3.900 3.900 AREA (cm2): 98.13                                         (cm):** 9.906 9.906                                                         **Effective dimensions due to corner crops                                    __________________________________________________________________________    CELL PARAMETERS         FACTOR                                                                             Voc                                                                              Isc                                                                              Vmp                                                                              Imp                                                                              Pmax                                 __________________________________________________________________________      BARE CELL BSR2  0.584 3.70 0.480 3.38 1.62                                    SERIES CELLS  2 1.168  0.960  3.24                                            PARALLEL CELLS  3  11.10  10.13 9.72                                          ASSEMBLY VOLTAGE  0.990 1.156  0.950                                          ASSEMBLY CURRENT  0.990  10.99  10.02 9.53                                    COVERGLASS UNCOATED  1.010  11.10  10.12 9.62                               Pstc SPM PARAMETERS (Pstc)       Efficiency @ 1367 W/m.sup.2                  LAPSS TEST       BOL @ 28 C  1.156                                                                            11.10                                                                            0.950                                                                            10.12                                                                            9.62                                                                      Eff = 11.95%                             Af SPECIFIED ARRAY-LEVEL LOSS                                                                         0.938                                                                              1.120                                                                            10.75                                                                            0.920                                                                            9.81                                                                             9.03                                   Sf SUN INTENSITY (Aphelion)  0.968  10.40  9.49 8.73                          Rf MICROMETEORITES  0.995  10.35  9.44 8.69                                   Rf UV  0.980 1.120 10.14 0.920 9.25 8.51                                      Rf RADIATION EFFECTS 1-MeV elect                                            Rf Voc   EOL     2.03E + 15                                                                           0.886                                                                              0.992                                              Rf Isc EOL 1.39E + 15 0.789  8.00                                             Rf Vmp EOL 2.03E + 15 0.886   0.815                                           Rf Imp EOL 1.39E + 15 0.784    7.25 5.91                                    Tfn TEMPERATURE (DEG C.)                                                                       56.06                                                          Tfn EOL TEMP COEFFICIENTS                                                   Tfn Voc (mV/C)                                                                         -2.28          -0.128                                                                             0.864                                              Tfn Isc (uA/C-cm2) 36  0.297  8.30                                            Tfn Vmp (mV/C) -2.02  -0.113   0.702                                          Tfn Imp (UA/C-cm2) 35  0.289    7.54                                                  5.29                                                                Pspm SPM PARAMETERS (Pspm)       Efficiency @ 1367 W/m.sup.2                  ON-ORBIT         EOL @ 56.06 0.864                                                                            8.30                                                                             0.702                                                                            7.54                                                                             5.29                                                                       Eff = 6.58%                             __________________________________________________________________________

                  TABLE 3B                                                        ______________________________________                                        Test Conditions                                                               ______________________________________                                        Performance at standard test                                                                     P.sub.STC                                                                            See Table 3A                                          conditions                                                                    Combined radiation factor Rf See Table 3A                                     Efficiency Eff See Table 3A                                                   Temperature coefficients Tfn See Table 3A                                     Front surface absorptance αf 0.71                                       Front surface hemispherical εf 0.87                                   emittance                                                                   ______________________________________                                    

The effective shielding was determined for both the front side and backside of the SPM. The values for the baseline design are given in Tables4 and 5.

                  TABLE 4                                                         ______________________________________                                        Front Shielding Calculation                                                     Material  Thickness     Volume Density                                                                          Areal Density                             ______________________________________                                        Microsheet                                                                            100 μm     2.605 gm/cm.sup.3                                                                         0.0265 gm/cm.sup.2                            CV7-2500  50 μm  1.01 gm/cm.sup.3 0.0051 gm/cm.sup.2                       Total 140 μm of fused silica  0.0316 gm/cm.sup.2                         ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        Back Shielding Calculation                                                      Material Thickness     Volume Density                                                                           Areal Density                             ______________________________________                                        Silicon                                                                              150 μm*    2.33 gm/cm.sup.3                                                                           0.0355 gm/cm.sup.2                            Array   0.0290 gm/cm.sup.2                                                    Total 290 μm of fused silica  0.0645 gm/cm.sup.2                         ______________________________________                                         *The 200 μm physical cell thickness equates to 150 μm shielding         thickness because of reduced red and infrared response in the cell base. 

The total mission fluence is established from the front and backshielding values given in Tables 4 and 5, respectively, and in FIG. 9.The results are shown in Table 6 below. It is noted that the Isc curveis used for all solar cell parameters for the back shielding case,consistent with the treatment of Table 6.1 of the Solar Cell RadiationHandbook. The degradation factors used in the power analysis are thentaken from Figures 3.55 to 3.59 of the Solar Cell Radiation Handbook.

                  TABLE 6                                                         ______________________________________                                        Total Mission Fluence                                                                      Isc       Voc,Pmax                                               ______________________________________                                        Front        8.20E + 14                                                                              1.46E + 15                                               Back 5.66E + 14 5.66E + 14                                                    Total 1.39E + 15 2.03E + 15                                                 ______________________________________                                    

A mass analysis for the SPM is shown in Table 7 below. Results of massmeasurements for prototype coverglass and silicon wafers, the dominantcomponents of the SPM, were used to validate the calculated values.

                  TABLE 7                                                         ______________________________________                                        Mass Analysis                                                                              Thick-        Unit         Total                                                                              % of                               SPM ness Area Mass Quantity Mass Total                                        Components (μm) (cm.sup.2) (gm) per SPM (gm) Mass                        ______________________________________                                        Silicon Solar                                                                          200     98.131  5.20  6      31.20                                                                              58.7                                 Cell                                                                        Solder   N/A (welded)                                                         Coverglass                                                                             100     609.868 16.141                                                                              1      16.14                                                                              30.4                                 Coverglass  50 98.131 0.503 6 3.02 5.70                                       Bonding                                                                       Adhesive                                                                      (CV7-2500)                                                                    Interconnects   0.155 18  2.79 5.20                                           Total     53.15 100.00                                                      ______________________________________                                    

The calculated reliability, R_(SPM), of the SPM is equal to thecalculated probability of success. The probability of success is relatedto component and weld joint failures. The solar cell failure rate, λ, isexpressed in units of "number of failures per operating hour." Thefailure rate of 1×10⁻⁹ failures per solar cell operating hour was usedbased on the JPL solar cell array design handbook.

A mission life of ten years and the on-orbit temperature of 56° C. wereused to determine the failure rate. The reliability predictions werecalculated for three scenarios: 1) two cells in series; 2) six cell inseries; and, 3) two cells in series and three in parallel.

The solar cell failure rate of 1×10⁻⁹ failures/hour is valid at 30° C.The on-orbit temperature was calculated to be 56° C. (see SPMperformance for details). The failure rate increases by 5% per 10° C.increase in temperature.

    56° C.-30° C.=26° C.

    26° C.×0.05=0.13

    λ cell=(1×10.sup.-9)×1.13=1.13×10.sup.-9 @56° C.

    R.sub.SPM =[e.sup.(-number of cells in series×λ cell×mission life in hours) ].sup.x

where x=number of cells in parallel

and where Mission Life=10 years×365 days/year×24 hours/day=87,600 hrs.

Scenario 1, 2 Cells in Series

    R.sub.SPM =[e.sup.(-2×1.13×10-9×87,600) ]

    R.sub.SPM =0.9998

Scenario 2, 6 Cells in Series

    R.sub.SPM =[e.sup.-6×1.13×10-9×87,600) ]

    R.sub.SPM =0.9994

Scenario 3, 2 Cells in Series by 3 in Parallel

    R.sub.SPM =[e.sup.-2×1.13×10-9×87,600) ].sup.3

    R.sub.SPM =0.9994

In summary, in at least one preferred embodiment, the SPM design ishighly reliable.

Cell Manufacture and Test

One example of a general solar cell manufacturing process is illustratedin FIG. 11. It is understood that other processes may be used as well.

(1) Wafer Etching 1102

In one preferred embodiment, wafers used in the SPM may be wire sawed.The wafers then undergo surface preparation. After sample inspection toverify compliance with size, thickness, resistivity, surface quality andcleanliness, the wafers are chemically etched to remove surfacecontaminants and damage from the sawing process. The wafers may be acidetched using automated production equipment to prepare the surface andcontrol wafer thickness. The front surface is preferably smooth and freeof work damage and provides for a shallow (0.15 μm) N+/P junction withgood characteristics. In a preferred embodiment, the back surface polishprovides high reflectance for longer wavelengths, reducing solarabsorptance giving lower on-orbit cell temperature. For the wraparound(WA) design, this etch method provides a well rounded edge for properdeposition of insulating layers and contact materials. Automatedhandling from coinstacked wafers to Teflon boats may be used. Thetransfer ensures that the two WA edges are etched and returned to acassette, with all edges correctly aligned. The post-etch waferthickness is controlled using SPC procedures which measure and controlthickness by etchant temperature, concentration and immersion time.

Preferably, the manufacturing equipment provides automation which allowsfor cassette-to-cassette wafer processing to achieve high throughput andyields.

(2) CVD SiO₂ Deposition 1104

In one embodiment, a diffusion mask is used on the back surface of thewafer prior to N+ diffusion to prevent doping of the back side of thewafer during the diffusion process, providing uniform and repeatableSiO_(x) layers. An ellipsometer is used to measure the oxide thicknessand the process is controlled by using SPC methods.

The CVD production equipment is available from Watkins-Johnson, and usesa continuous belt process with automatic cassette-to-cassette loaders.The wafers are transported through the furnace on a belt where silaneand oxygen are mixed to form SiO₂ on the heated back surface of thewafers. The loaders allow for high throughput and high yields.

(3) The Diffusion Process 1106

Diffusion is the primary technique for forming the shallow N+/Pjunction. The wafers are semi-automatically transferred frompolypropylene cassettes into a quartz diffusion boat. A transfer deviceis used to transfer the wafers to minimize wafer chipping and breakageand to maintain the alignment of the designated WA edges. The solar celljunction is formed in clean quartz boats and tubes. Phosphorusoxichloride (POCl₃) and oxygen are used to form phosphorus pentoxide (P₂O₅) on the surface of the wafers. The high temperature (≈850° C.) drivesthe phosphorus into the wafer to form the junction. The sheet resistanceof the diffused layer is controlled using SPC methods. This controlensures proper junction depth and therefore the good cell performance,both before and after orbital irradiation.

The MRL production rate diffusion furnace uses advanced process controlcapability to control diffusion depths and sheet resistance values.Quartz boats are manually loaded on a quartz paddle to start theprocess. The computer control system automatically positions the wafersin the hot zone of the furnace, initiates the proper gas flow sequence,and slowly transfers the wafers out of the process tube to cool. Thewafers are then transferred back to polypropylene boats.

(4) Oxide Etch Process 1108

This process removes the oxide formed during the diffusion mask process(CVD) and removes the thin glassy oxides formed during the diffusionprocess. The etching solution uses a mixture of hydrofluoric acid anddeionized water.

The oxide etch process is totally automatic and uses the same equipmenttype as for acid etch. Wafers are staged at the front of the machine incassettes. The machine picks up the cassettes and automaticallyprocesses them through the etch and rinse steps. It also automaticallyloads and replenishes the chemicals using a chemical dispense system.

(5) CVD SiO₂ for Dielectric 1110

A dielectric oxide is preferably formed on the edges of the wafers,where the WA metal is deposited, to prevent shorting of the P/Njunction. The dielectric is formed in the WA areas using CVD SiO₂.Mechanical masks are used to define the pattern for isolation of theN-contact on the front and back sides of the wafers. The oxide thicknessis controlled using SPC criteria.

The Watkins-Johnson machine is the same type as used for CVD of SiO₂ forthe diffusion mask process. It is a reliable, continuous belt process.The operator positions a mask properly on a wafer, and clamps it with aclip. The wafer and mask assemblies are manually placed on the belt ofthe CVD SiO₂ furnace, and SiO₂ is deposited in the designated WA areas.

(6) Front/Back Metal Evaporation 1112, 1114

Front (TiPdAg) and back (AlTiPdAg) metal contact depositions areperformed in high volume vacuum deposition evaporators used extensivelyfor space cell manufacturing. CHA Industries Mark 50 vacuum depositionsystem is specifically designed for flexibility and long termreliability to support high volume production. Precision metal masks,with ≈50 wide grid openings, are used to form the front grid and bus barpattern. The mask maintains cell performance while eliminating the usualexpensive, labor intensive photolithography processing. A mask is alsoused for the back side to ensure the proper electrical isolation neededon the back side between the P and N metal contacts. The metal thicknessare controlled using SPC methods.

(7) Antireflective (A/R) Coating Process 1116

The cells are coated with an atmospheric pressure chemical vapordeposited (CVD) antireflective coating on the front surface. The coatingoperation is a low cost, high volume, continuous belt process usingequipment provided by BTU International. Vaporizedtetraisopropyltitanate (TPT) and water are mixed and introduced to theheated surface of the wafers where TiO₂ is formed. With the WA celldesign, masks are not required to shield the contacting areas from theAR coating for additional cost reduction.

(8) Sintering Process 1118

Contact and coating sintering is performed to form good ohmic contact tothe cell and to increase adhesion to the silicon wafer. The AR coatingadhesion is also improved. Sintering uses a belt furnace supplied by theThermco Company. Hydrogen and nitrogen are mixed in the furnace tominimize oxidation of the metals during the process. The wafers areplaced directly on the moving belt, and process controllers ensure thatthe correct heating rate, dwell time and cooling rate are maintained foroptimum contact sintering. The wafers are then removed from the belt andplaced in coin stacks.

(9) Cell Lot # Marking 11120

Traceability of each evaporation lot is established using a TECSTARstandard high volume, non-contact VideoJet marking system. Other markingsystems may also be used.

(10) Cell Electrical Test 11122

Solar cells are tested with automated cell test equipment incorporatingan integrated AM0 solar simulators. The cells are separated intoelectrical groups based on their individual outputs measured at aconstant test voltage.

Coin stacks of cells are placed in a load stacker magazine on thetester. A robotic transfer system automatically places the cells underthe solar simulator for testing, and then places the cells in the properelectrical group. The operator only needs to pick up the counted stacksof tested cells and to identify electrical groups. The sorted cells aretransferred to the assembly area for assembly into SPMs.

SPM Manufacture and Test

One technique for manufacturing SPMs is illustrated in the SPMManufacturing Flow diagram of FIG. 12. It will be understood by oneskilled in the art that other known techniques may be used as well. Thedetailed descriptions of the individual SPM processing steps arecontained in the following paragraphs.

(1) Load Cell Pallet 1202

An automated cell handling system is used to provide the accuracy andrepeatability needed for high volume assembly.

Cells may be robotically removed from a cassette and positioned on asix-cell fixture (cell pallet) that maintains the cell alignmentthroughout the glassing process. Only minimal mechanical contact withthe active surface of the cell occurs. Contact of the cells edges andthe active surfaces with metal surfaces is eliminated. Unlike a standardfront-to-back contact cell, no handling steps involving awkward "tabbed"cells are required.

The positioning and adhering of the cell onto a cell pallet removespossible inherent cell bow in addition to maintaining the cell'slocation with respect to the other five cells. Varying cell gaps due tocell dimensional tolerances become less critical when interconnects donot pass through them. Having no interconnects on the cell back enablesthe cells to be placed flat against the pallet for precise control ofthe adhesive and SPM assembly thickness.

The automated rotation (180° flip) of the loaded cell pallet, followedby the cell's self-aligning placement onto a glass pallet containing acoverglass with glassing adhesive, completes this process step.

(2) Load Glass Pallet 1204

Manual removal of coverglass from its shipping container provides adependable and expedient method of separation from the protectivepacking materials. Next, a cleaning process (nitrogen blow-off) andvisual inspection provides screening for potential material defects. Thesix-cell coverglass is then aligned onto a glass pallet designed toretain its position and protect the glass edges from subsequent damage.The pallet is also designed to reduce or eliminate material "bowing"throughout the glassing process. Maintaining the cells and thecoverglass flat to the fixture surfaces is helpful in controlling theadhesive gap during the "wicking" and adhesive cure processes. Thetransfer and alignment of the pallet onto the adhesive deposit stationcompletes this process step.

(3) Adhesive Deposit On Glass 1206

Manual adhesive preparation, documentation and equipment calibrationhave been proven effective for high-volume production. Standardprocedures emphasize attention to material pot life and storageconditions. Adhesive materials are packaged in precise mix ratios foraccuracy. Prior to dispensing, the adhesive mix is "de-gassed" in avacuum chamber to remove entrapped air and minimize voids duringglassing.

An adhesive pattern is deposited onto the coverglass surface with theprecision control of a programmed X-Y table in concert with a multi-headadhesive metering system for consistent placement and repeatable volumedispensing. Transfer of the glass pallet containing a coverglass withglassing adhesive completes this process step.

(4) Adhesive Cure 1208

The cell/adhesive/glass sandwich is automatically transferred to aconveyor where adhesive "wicking" progresses under ambient conditionsunder the weight of the cell pallet. The cell pallet remains alignedwith the glass pallet via guide pins which allow the sandwich to cometogether until the cell pallet bottoms-out on the glass pallet and theadhesive gap is fixed. Even with adhesive viscosity changes over theallowable pot life of the material, full wicking is achieved in the timeallotted. Any excess adhesive flows into the gaps between the cells.Without any interconnects attached to the cell's active side, theadhesive gap design is the thinnest and produces the lightest overallweight. The option of glassing with EVA produces an excessive 0.013 cmcell/coverglass gap due to sheet material thickness limitations, soselected liquid silicones with thickness capabilities down to 0.003 cmare preferable. Since interconnects in this area would inhibit andcomplicate adhesive flow, trap unwanted air and promote cell surfacehighspots that may come in contact with the glass, alternatives to theWA cell design are less desirable during this process.

At the end of the wicking operation, the fixture assembly passes througha tunnel oven profiled to bring each fixture up to temperaturegradually, to thus prevent warping of the assembly or uneven cure of theadhesive. The conveyor belt width is oversized to allow a large range ofadjustment without limiting throughput. The end of the conveyor passesthrough a cooling section designed to bring the assembly back to ambientconditions without stressing the SPM. The conveyor system ensures thateach SPM is exposed to identical process parameters unlike a batch ovensystem that is subject to the human variable. To end this process step,the cell pallet is removed from the assembly, leaving the glass palletcontaining the module to be manually transferred to the interconnectingstation.

(5) Interconnect And Inspect 1210

Automated interconnection technology is used to mechanically formindividual interconnects from a reel of ribbon and then roboticallyposition them for welding. Redundant welding performed withstate-of-the-art "constant power" controlled equipment ensures superiorreliability and weld strength consistency by automatically adjusting tovariances in cell/interconnect surface conditions via process feedback.All portions of the interconnect, including the formed strain relief andwelded areas, are fully exposed and free from adhesive contaminationunlike any of the front to back contact options. When contact must bemade to the front side of a cell, the interconnects strain relief andweld joints become buried in adhesive during the glassing process,prompting concern with having to endure differential thermal stressesbetween the front and back-side of the cell. By contrast, welding solelyto the cell back-side after glassing, in accordance with one embodimentof the present invention, creates intimate support of every portion ofthe cell with an adhesive/glass layer producing the lowest mechanicalstresses. Welding to a cell's front side typically requires apre-glassing weld station, and special handling of interconnected cells,causing increased attrition and manufacturing difficulties. A weldstation also attaches the necessary array interconnects to the SPM asdetailed above. After welding, an integrated visual inspectionidentifies candidates to be separated for rework on another weld stationto prevent any interruption in product flow. The SPM is then separatedfrom the glassing pallet and transferred to the cleaning station.

(6) Clean, Electrical Test And Mark 1212

Manual cleaning of SPM coverglass utilizing process compatible solventsto remove adhesive contamination is performed as required. Unlikesoldered interconnects, welding leaves no contaminating residue.Additionally, the process used for attaching interconnects afterglassing eliminates clean-up which would otherwise be necessary due toadhesive wicking along the interconnect into its strain relief region.The next step is to position the SPM glass-side down on the electricaltest fixture. Automated probing of the electrical contacts, flashtesting, data collection/storage and marking of the SPM with bar-codeand human readable codes are completed at this station to guaranteetraceability and minimize further handling steps prior to the inspectionprocess.

(7) Inspection 1214

Visual in-process inspection is performed by line operators. Finalinspection of the SPM may be independently performed by qualityassurance personnel in accordance with an approved Acceptance Test Plan.

(8) Packaging 1216

Completed SPMs are packaged in reusable containers designed formechanized loading/unloading.

While certain preferred embodiments of the invention have beendescribed, these embodiments have been presented by way of example only,and are not intended to limit the scope of the present invention.Accordingly, the breadth and scope of the present invention should bedefined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. An AM0 radiation tolerant solar cell array modulewhich can be efficiently assembled into a larger solar panel to generatepower for a spacecraft, said AM0 radiation tolerant solar cell arraymodule comprising:at least a first single crystal solarcell having afirst back side and a first front side and a second single-crystal solarcell having a second front side and a second back side, at least one ofsaid first single-crystal solar cell and said second single-crystalsolar cell having a shallow junction N on P structure, and wherein saidfirst single crystal solar cell is a discrete component said secondsingle crystal solar cell is a discrete component; a first contactformed on at least the first back side of said first single-crystalsolar cell; a second contact formed on at least the second back side ofsaid second single-crystal solar cell; a conductor in electricalcommunication with said first contact and said second contact; a thirdcontact coupled to said first single-crystal solar cell, said thirdcontact couplable to another AM0 radiation tolerant solar cell arraymodule; a ceria-doped cover overlaying said first single-crystal solarcell and said second single-crystal solar cell, said cover remainingsubstantially transparent when exposed to an AM0 space radiationenvironment, said cover configured to allow light to pass through thecover to reach at least said portion of each of said firstsingle-crystal solar cell and said second single-crystal solar cell; andan adhesive positioned between said cover and said first single crystalsolar cell and said second single crystal solar cell.
 2. The AM0radiation tolerant solar cell array module as defined in claim 1,wherein at least one of said first single-crystal solar cell and saidsecond single-crystal solar cell is formed from a material includingsilicon.
 3. The AM0 radiation tolerant solar cell array module asdefined in claim 2, wherein said material has a base resistivity of lessthan 10 ohms-cm.
 4. The AM0 radiation tolerant solar cell array moduleas defined in claim 1, wherein at least one of said first single-crystalsolar cell and said second single-crystal solar cell is formed from atleast GaAs.
 5. The AM0 radiation tolerant solar cell array module asdefined in claim 1, said radiation tolerant solar cell array modulehaving a power-to-mass ratio of at least 100 W/kg.
 6. The AM0 radiationtolerant solar cell array module as defined in claim 1, said radiationtolerant solar cell array module having an areal power density of atleast 87 W/m².
 7. The AM0 radiation tolerant solar cell array module asdefined in claim 1, wherein at least one of said first single-crystalsolar cell and said second single-crystal solar cell is a multijunctionsolar cell.
 8. The AM0 radiation tolerant solar cell array module asdefined in claim 1, wherein said first contact wraps around from saidfirst front side to said first back side.
 9. The AM0 radiation tolerantsolar cell array module as defined in claim 1, wherein at least one ofsaid first single-crystal solar cell and said second single-crystalsolar cell is no greater than 200 μm thick.
 10. A method of assemblingan AM0 radiation tolerant solar cell array module suitable for use inspace, said method comprising:selecting at least two discrete shallowjunction solar cells, each of said two discrete shallow junction solarcells having corresponding front sides and back sides; selecting aceria-doped cover having a cover back side and a cover front side;placing an adhesive on at least one of said front sides of said twodiscrete shallow junction solar cells and said cover back side; andoverlaying at least a portion of each of said two discrete shallowjunction solar cells with said cover so that said adhesive bonds saidcover to said at least two discrete shallow junction solar cells. 11.The method of assembling a solar cell array module as defined in claim10, further comprising:forming a first contact on at least said backside of a first discrete shallow junction solar cell of said at leasttwo discrete shallow junction solar cells; and forming a second contacton at least said back side of a second discrete shallow junction solarcell of said at least two discrete shallow junction solar cells.
 12. Themethod of assembling a solar cell array module as defined in claim 11,further comprising interconnecting said first contact and said secondcontact.
 13. The method of assembling a solar cell array module asdefined in claim 12, further comprising:forming a third contact on atleast said back side of said first discrete shallow function solar cell,wherein said first contact is coupled to a first polarity of said firstdiscrete shallow junction solar cell and said third contact is coupledto a second polarity of said first discrete shallow junction solar cell;and forming a fourth contact on at least said back side of said seconddiscrete shallow junction solar cell wherein said second contact iscoupled to a first polarity of said second discrete shallow junctionsolar cell and said fourth contact is coupled to a second polarity ofsaid second discrete shallow junction solar cell.
 14. The method ofassembling a solar cell array module as defined in claim 13, furthercomprising interconnecting said first and said fourth contacts.
 15. Themethod of assembling a solar cell array module as defined in claim 12,further comprising welding a conductor to said first and said secondcontacts.
 16. The method of assembling a solar cell array module asdefined in claim 12, further comprising soldering a conductor to saidfirst and said second contacts.
 17. The method of assembling a solarcell array module as defined in claim 12, further comprisingmechanically bonding a conductor to said first and said second contacts.18. The method of assembling a solar cell array module as defined inclaim 12, further comprising placing a ribbon conductor in electricalcommunication with said first contact and said second contact.
 19. Themethod of assembling a solar cell array module as defined in claim 12,further comprising applying an anti-reflective coating on said cover.20. A solar cell array module suitable for use in space, said solar cellarray module comprising:at least two interconnected solar cells, each ofsaid at least two interconnected solar cells having an AM0 radiationtolerant semiconductor structure; and a ceria-doped cover overlaying atleast a portion of each of said at least two interconnected solar cells,said cover configured to allow light to pass through the cover to reachsaid at least a portion of each of said two interconnected solar cells.21. The solar cell array module as defined in claim 20, furthercomprising:a first contact located on a back of a first of said at leasttwo interconnected solar cells; a second contact located on a back of asecond of said at least two interconnected solar cells; and aninterconnect coupled to said first contact and said second contact. 22.The solar cell array module as defined in claim 21, further comprising:athird contact located on said back of said first of said at least twointerconnected solar cells; a fourth contact located on said back ofsaid second of said at least two interconnected solar cells; and aninterconnect coupled to said third contact and said fourth contact. 23.The solar cell array module as defined in claim 20, wherein at least oneof said at least two interconnected solar cells utilizes single-crystalsilicon qualified for use in at least an AM0 radiation environment. 24.The solar cell array module as defined in claim 23, wherein saidsingle-crystal silicon has a base resistivity of less than 10 ohms-cm.25. The solar cell array module as defined in claim 20, wherein at leastone of said at least two interconnected solar cells utilizes GaAs. 26.The solar cell array module as defined in claim 20, wherein at least oneof said at least two interconnected solar cells is a multijunction solarcell.
 27. The solar cell array module as defined in claim 20, furthercomprising at least one two-sided wraparound contact which wraps from afront side to a back side of at least one of said at least twointerconnected solar cells.
 28. The solar cell array module as definedin claim 27, wherein said at least one two sided wraparound contactoccupies less than 5% of said back side of said interconnected solarcell.
 29. The solar cell array module as defined in claim 27, whereinsaid at least one two-sided wraparound contact is formed from at leastTiPdAg.
 30. The solar cell array module as defined in claim 20, whereinat least one of said at least two interconnected solar cells is nogreater than 200 μm thick.
 31. The solar cell array module as defined inclaim 20, further comprising at least one bypass diode coupled to atleast one of said at least two interconnected solar cells.
 32. The solarcell array module as defined in claim 20, wherein at least one of saidat least two interconnected solar cells has an efficiency of greaterthan 12%.
 33. The solar cell array module as defined in claim 20,wherein at least one of said at least two interconnected solar cells hasan efficiency of greater than 24%.
 34. The solar cell array module asdefined in claim 20, wherein said at least two interconnected solarcells are interconnected using an interconnect having a thermalcoefficient of expansion compatible with a thermal coefficient ofexpansion of at least one of said at least two interconnected solarcells.
 35. The solar cell array module as defined in claim 20, whereinat least one of said at least two interconnected solar cells has an areaof at least 100 cm².
 36. The solar cell array module as defined in claim20, further comprising at least one contact for interconnection to atleast a second solar cell array module.
 37. The solar cell array moduleas defined in claim 20, wherein said at least two interconnected solarcells are connected in series.
 38. The solar cell array module asdefined in claim 20, wherein said at least two interconnected solarcells are connected in parallel.
 39. The solar cell array module asdefined in claim 20, wherein said cover is ceria-doped.
 40. The solarcell array module as defined in claim 20, further comprising ananti-reflective coating overlaying at least a portion of said cover. 41.The solar cell array module as defined in claim 20, wherein said coverincludes potassium ions.
 42. The solar cell array module as defined inclaim 20, further comprising a silicone-type adhesive which bonds saidcover to said at least two interconnected solar cells.
 43. The solarcell array module as defined in claim 42, wherein said adhesive is aethylene vinyl acetate type adhesive.
 44. The solar cell array module asdefined in claim 20, wherein said cover is at least 600 cm².
 45. Thesolar cell array module as defined in claim 20, said solar cell arraymodule having a power-to-mass ratio of at least 100 W/kg.
 46. The solarcell array module as defined in claim 20, said solar cell array modulehaving an areal power density of at least 87 W/m².
 47. The solar cellarray module as defined in claim 20, wherein said AM0 radiation tolerantsemiconductor structure includes at least a radiation resistant, shallowjunction N on P structure.
 48. The solar cell array module as defined inclaim 47, wherein said cover is transparent.
 49. The solar cell arraymodule as defined in claim 20, further comprising:a first polarity of afirst of said at least two interconnected solar cells; a second polarityof said first of said at least two interconnected solar cells; a firstcontact coupled to said first polarity; and a second contact coupled tosaid second polarity.
 50. The solar cell array module as defined inclaim 49, wherein said first contact and said second contact are mountedon a same side of said first of said at least two interconnected solarcells.
 51. The solar cell array module as defined in claim 49, whereinsaid first contact is mounted on a first side of said first solar celland said second contact is mounted on a second side of said first ofsaid at least two interconnected solar cells.
 52. An AM0 radiationtolerant solar cell assembly for use in a space environment, said solarcell assembly comprising:a first solar cell; a second solar cellinterconnected to said first solar cell; a first ceria-doped coveroverlaying at least a portion of each of said first and second solarcells; a third solar cell; a fourth solar cell interconnected to saidthird solar cell; a second ceria-doped cover overlaying at least aportion of each of said third solar cell and said fourth solar cell; anda first interconnect coupled to at least one of said first solar celland said second solar cell and at least one of said third solar cell andsaid fourth solar cell.
 53. The solar cell assembly as defined in claim52, wherein at least one of said first solar cell, said second solarcell, said third solar cell and said fourth solar cell includes aradiation resistant, shallow junction N on P structure.
 54. The solarcell assembly as defined in claim 52, further comprising at least afirst contact and a second contact, both of said first contact and saidsecond contact overlaying at least a portion of a back side of one ofsaid first solar cell, said second solar cell, said third solar cell,and said fourth solar cell, wherein said first contact is coupled to afirst solar cell polarity and said second contact is coupled to a secondsolar cell polarity.
 55. An AM0 radiation tolerant solar cell arraymodule means for assembly into a larger solar panel, said radiationtolerant solar cell array module means comprising:a first means forconverting solar energy into electrical energy, said first means havinga first radiation resistant structure, wherein said first means forconverting solar energy is useable in an AM0 spectrum; a first contactmeans for coupling said first means for converting solar energy to ameans for interconnection, said first contact means disposed on saidfirst means for converting solar energy; a second means for convertingsolar energy into electrical energy, said second means having a secondradiation resistant structure, wherein said second means for convertingsolar energy into electrical energy is useable in an AM0 spectrum; asecond contact means for coupling said second means for converting solarenergy into electrical energy to said means for interconnection, saidsecond contact means disposed on said second means for converting solarenergy into electrical energy; an AM0 radiation tolerant ceria-dopedcover glass for protecting said first means for converting solar energyinto electrical energy and said second means for converting solar energyinto electrical energy; and an AM0 radiation tolerant means for adheringsaid AM0 radiation tolerant cover glass to at least a portion of saidfirst means for converting solar energy into electrical energy and saidsecond means for converting solar energy into electrical energy.